1. Field of the Invention
The present invention concerns a photointerruptor for use in an optical transmission-type rotary encoder comprising a rotatable pulse scale having a code pattern formed thereon and a light emitting optical fiber and a light receiving optical fiber which are secured to a housing with the end faces of them being opposed to each other on both sides of the code pattern.
2. Description of the Prior Art
A photointerruptor for use in an optical transmission-type rotary encoder in the prior art comprises a structure, for example, as shown in FIG. 4, in which a housing H is made of a synthetic resin and provided with a pulse scale passing groove or slit 2 for allowing a pulse scale 1 having a code pattern C to rotatably pass through the groove. Mounting apertures 41 and 42 are perforated from both surfaces to the side wall of the groove 2 and a light-emitting optical fiber 3 and a light-receiving optical fiber 4 are inserted through the mounting apertures 41 and 42 such that their end faces 3a and 4a are opposed to each other on both sides of the code pattern C of the pulse scale 1.
Then, the photointerruptor is situated to a predetermined position, such that the end faces 3a and 4a of the respective optical fibers 3 and 4 are opposed to each other on both sides of the code pattern C formed in the pulse scale 1.
In the optical transmission-type rotary encoder described above, since the optical path between the light-emitting optical fiber 3 and the light-receiving optical fiber 4 is formed and shut intermittently by the code pattern C formed on a rotating pulse scale 1, predetermined pulse signals are outputted in accordance with the angle of rotation of the pulse scale. In the photointerruptor, if the end faces 3a and 4a of the light-emitting optical fiber 3 and the light-receiving optical fiber 4 attached to the interruptor are injured or contaminated, the optical pulses outputted in accordance with the angle of rotation can no more be detected accurately.
In the prior art, the end faces 3a and 4a of the light-emitting optical fiber 3 and the light-receiving optical fiber 4 are at first fixed, for example, by means of adhesives being protruded slightly to the inside of the groove 2 and then the end faces are polished by passing an abrasive-coated paper or cloth through the passing groove 2. Alternatively, light-emitting optical fiber 3 and light-receiving optical fiber 4 are previously polished and then inserted into and bonded to the mounting apertures 41 and 42 of the housing H.
However, the polishing operation for the end faces of the optical fibers 3 and 4, while putting them at the inside of the pulse scale passing groove 2, has been difficult, since the gap of the groove 2 is usually as narrow as only about 1.5 mm. In addition, it is also difficult to judge whether the polishing has been conducted satisfactorily or not by confirming the state at the end faces.
In a case of using previously polished optical fibers, since the end faces may be scratched or contaminated with adhesives during the fiber-mounting operation, it is necessary to confirm the state of the end faces after the completion of the mounting operation. However, since the gap of the pulse scale passing groove 2 is narrow, it is difficult to visually observe the state of the end faces and it has been actually difficult to confirm whether the end faces are injured or contaminated.
Accordingly, the polishing operation inevitably requires too much time and labor and this increases the production cost. In addition, even when the polishing has been conducted at the expense of such long time and much labor, since the finishing state can not be confirmed, it is difficult to keep the quality of the optical transmission-type rotary encoder always at a predetermined level.